Biophotonics_Concepts_to_Applications

Example 9.12Consider a PCS test for examining a hemoglobin molecule

that is diffusing in water. (a) If D = 1× 10 −^6 cm^2 /s for hemoglobin in water

and ifη=1× 10 −^3 N s/m^2 for water, what is the hydrodynamic diameter of

the hemoglobin molecule? (b) How does the volume of the equivalently

diffusing sphere compare with the actual volume of 321.6 nm^3 for a hemo-

globin molecule?

Solution:

(a) From Eq. (9.10), the hydrodynamic diameter is

dH¼

ðÞ 1 : 38  10 ^23 J=KðÞ293 K

3 pðÞ 1 : 0  10 ^3 Ns=m^2 ðÞ 0 : 1  10 ^9 m^2 =s

¼ 4 :29 nm

(b) The volume of the equivalent sphere is

V¼

4 pðdH= 2 Þ^3

3

¼

4 pð 2 :15 nmÞ^3

3

¼ 41 :3nm^3

9.11 Fourier Transform Infrared Spectroscopy

Fourier transform infrared (FTIR) spectroscopyis used to determine how much
light a material sample emits (from luminescence or Raman scattering) or absorbs at
each wavelength in a broad spectral range [ 56 – 58 ]. The information that can be
deduced from the FTIR spectrum include an identification of the material sample, a
measure of the consistency or quality of a material, and a determination of the
amount of specific compounds in a mixture. Some key advantages and features of
FTIR include the following:

• It is a nondestructive measurement and analysis method


• It provides a precise measurement method that requires no external calibration


• The signal-to-noise ratio of the spectral display is a factor of 100 better than that
  of previous generation spectrometers


• It has a high wavenumber measurement accuracy of±0.01 cm−^1


• Information from all wavelengths is collected simultaneously in scan times of
  less than a second


• It has a wide scan range of 1000–10 cm−^1
  As shown in Fig.9.21, the FTIR spectrometer consists of a collimated laser
  source, an interferometer component consisting of a beam splitter and two mirrors,
  a sample compartment, a photodetector for capturing the optical signal,

284 9 Spectroscopic Methodologies